Relevant research papers

The claims made throughout this Codex rest on published work, most of it peer-reviewed and much of it freely readable. This is a curated reading list, grouped so that each heading states what the papers under it actually establish. That structure matters: the evidence for the field's premise, the evidence that structure survives preservation, and the evidence that function returns are three different things at three different strengths, and running them together is the most common way this subject gets oversold.

Where a paper is co-authored by someone at Tomorrow.bio or at a partner organisation, it is marked. The point of a reading list is that you can check it, which requires knowing who wrote what.

The premise the field rests on

Cryonics proceeds on the premise that long-term memory and identity are encoded in durable physical structure, principally the pattern of neuronal connections and synaptic strengths, rather than in ongoing electrical activity. This is a premise, not a demonstrated result, and its support is best described as the majority position among neuroscientists, without being settled in its details. The concept is discussed in memory, identity and the brain.

• What are memories made of? A survey of neuroscientists on the structural basis of long-term memory (Zeleznikow-Johnston, Kendziorra and McKenzie, PLOS ONE, 2025). Of 312 neuroscientists surveyed, 70.5% agreed that long-term memories are primarily maintained by neuronal connectivity patterns and synaptic strengths. The same survey found no clear consensus on which specific neurophysiological features carry the information. This measures expert opinion, not preservation outcomes. Disclosure: co-authored by Emil Kendziorra, CEO of Tomorrow.bio and author of this article.

What has been preserved

These papers report structural outcomes: what the tissue looked like, at what resolution, after preservation. This is the strongest body of evidence in the field.

• Aldehyde-Stabilized Cryopreservation (Song and Fahy, Cryobiology, 2015). The 21st Century Medicine method that won the Brain Preservation Foundation's prizes, preserving traceable synaptic connectivity across whole rabbit and pig brains. Glutaraldehyde fixes the ultrastructure first, then perfusion with 65% ethylene glycol allows cooling without ice. Note the trade: fixation preserves structure and forecloses biological revival of that tissue.
• Ultrastructural and Histological Cryopreservation of Mammalian Brains by Vitrification (Fahy, Spindler, Wowk et al., 2026). Whole-brain ultrastructure preserved by vitrification alone, without prior aldehyde fixation. Preprint, not yet peer reviewed.
• Cryopreservation of brain cell structure: a review (McKenzie et al., Free Neuropathology, 2024). A review of 97 studies on how preservation methods affect brain structure, including where current techniques fall short.
• Structural brain preservation: a potential bridge to future medical technologies (McKenzie et al., Frontiers in Medical Technology, 2024). Argues that current methods have a non-negligible chance of success and merit research. Co-authors include Aschwin de Wolf of Advanced Neural Biosciences and Ariel Zeleznikow-Johnston.

What has recovered function

A step beyond structure: tissue that worked again after preservation. Every result here is bounded by its species and its scale, and those bounds are the load-bearing part.

• Functional recovery of the adult murine hippocampus after cryopreservation by vitrification (German et al., PNAS, 10 March 2026). Mouse hippocampal slices, and whole brain in situ, held below the glass transition for up to seven days, then rewarmed. Structural integrity, metabolic responsiveness, neuronal excitability, synaptic transmission and long-term potentiation all recovered. LTP reached 138.06 ± 6.90% against 157.68 ± 7.14% in controls, P = 0.072, from seven and eight slices across seven mice; not a significant difference, though the sample is too small to exclude a real one. The authors describe it as short-term recovery. PNAS published an independent commentary in June 2026.
• Physical and biological aspects of renal vitrification (Fahy et al., Organogenesis, 2009). A rabbit kidney vitrified, rewarmed, transplanted, and shown to function as the animal's only kidney. The landmark demonstration that a whole complex organ can complete the cycle.
• Persistence of Long-Term Memory in Vitrified and Revived Caenorhabditis elegans (Vita-More and Barranco, Rejuvenation Research, 2015). Nematodes retained a learned olfactory association through vitrification and revival. The organism has 302 neurons. This is evidence that a stored association can survive vitrification in a very simple nervous system, and it is not evidence about mammalian memory.

What has not been shown

No study has demonstrated that memory or identity survives preservation in a human brain. No study has demonstrated functional recovery of a whole mammalian brain, as opposed to slices and short-duration whole-brain preparations. No preservation performed on a human patient has been reversed. Cryoprotectant toxicity means viability is currently believed to be lost during cryoprotective perfusion even in good cases, so preserving ultrastructure and preserving a living brain are, today, different achievements. The case for cryonics is an argument from preserved structure plus the premise above, not a demonstrated result, and any source that presents it otherwise is overselling it.

Rewarming and scale

• Sound waves for solving the problem of recrystallization in cryopreservation (Alcalá, Risco et al., Scientific Reports, 2023). High-intensity focused ultrasound for rapid volumetric rewarming, one of two approaches to the rewarming bottleneck.
• Vitrification and nanowarming of kidneys (Han et al., Nature Communications, 2023). Rat kidneys vitrified, stored up to 100 days, rewarmed by nanoparticle excitation, transplanted, and life-sustaining. The other approach, and the one that has since been pushed to litre-scale volumes.

Roadmaps and forecasts

• Biostasis: A Roadmap for Research in Preservation and Potential Revival of Humans (McKenzie et al., Brain Sciences, 2024). The research agenda: better protocols, quality metrics, and the factors around cardiac arrest that determine case quality. Disclosure: co-authors include Brian Wowk and Emil Kendziorra, author of this article.
• Practitioner forecasts of technological progress in biostasis (McKenzie et al., 2025). Twenty-two practitioners forecast the field's challenges and candidate revival strategies. Useful because it records disagreement and uncertainty rather than resolving it. Preprint.
• Winter is coming: the future of cryopreservation (Bojic et al., BMC Biology, 2021). An interdisciplinary review of the real obstacles: scaling to large volumes, preventing ice, and reducing cryoprotectant toxicity.

The wider context

• Cryopreservation of Oocytes and Embryos (Dhali et al., 2018). Cryopreserving human cells is routine clinical practice. The open question for a brain is scale and complexity, not principle.
• Sleuthing subjectivity: a review of covert measures of consciousness (Kronemer et al., Nature Reviews Neuroscience, 2025). On detecting consciousness, relevant to how a revived mind could ever be assessed.
• Survey of US internet users' sentiments towards cryopreservation (Gillett et al., PLOS ONE, 2021). On the gap between awareness and participation.

Procedures and essays

• Human Cryopreservation Procedures (Aschwin de Wolf and Charles Platt, revised 2023, fact-checked by Brian Wowk). The standard operational reference: stabilization, perfusion, cooling, storage, and the quality-control doctrine requiring CT scans and electron micrographs in every case report. Much of the technical detail in this Codex traces back to it.
• Scientists' Open Letter on Cryonics. Signed by dozens of researchers, stating that cryonics is a legitimate science-based endeavour. A statement of position, not a result.
• A Skeptic's Guide to Cryonics (Aschwin de Wolf). Argues the case on skeptical rather than faith-based grounds.
• Cryostasis Revival (Robert Freitas, 2022). A detailed proposal for how nanomedicine might repair and revive a patient. A theoretical exercise, not a demonstrated route.
• Tim Urban's essays. The most readable introduction to the underlying questions.

Further reading

• Advancing the field
• Memory, identity and the brain
• How we might achieve revival
• Arguments against cryonics